The present invention relates to a laminated film having a releasing property, specifically to a releasing film suitable for manufacturing a multilayered printed circuit board and to a carrier film for manufacturing a coating film.
A releasing laminated film is used as a releasing film for making multilayered printed circuit boards or for embossing leather grains on synthetic leather. It is also used as a carrier film for producing a coating film, or as a protective film for protecting a tacky or adhesive film from dusts, which protective film is peeled from the tacky or adhesive film immediately before using them.
A multilayered printed circuit board is produced by stacking a plurality of printed circuit boards with prepregs inserted therebetween, and sandwiching the deck of circuit boards thus obtained with releasing films and, then, hot pressing the deck to melt the prepregs, followed by hardening the prepregs to integrate the deck. As the releasing film, a fluororesin film is used, for example, poly(vinyl fluoride) film at a temperature of 175xc2x0 C. or lower, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) at a temperature higher than 175xc2x0 C.
There is such a problem concerning printed circuit boards having blind through-holes that a portion of molten prepregs bleeds out through openings of the through-holes of the topmost board upon hot-pressed and hardens on copper foil to thereby prevent the copper foil to be etched off, so that an accurate circuit may not be formed on the circuit board surface. To solve this problem, a thicker releasing film having a thickness of 0.06 to 0.3 mm than conventional films is used as described in Japanese Patent Application Laid-open H5-283862. However, such a thick film of the aforesaid fluororesin such as poly(vinyl fluoride) is generally expensive to raise production costs, which offsets an effect of decrease in a defection rate of the printed circuit boards. In addition, the fluororesin films such as poly(vinyl fluoride) film inherently have low stiffness or lack firmness.
Another problem with the conventional films is that they have poor handling property when placed on the printed circuit boards.
In addition, if there is a foreign body between a hot press plate or an embossing role and a releasing film when pressure is applied, a shape of the foreign body is transferred to cause a dent or mark on a circuit board surface through the releasing film due to the film""s insufficient firmness. Such a dent may cause an inaccuracy in a circuit or embossed pattern.
Moreover, conventional releasing films are difficult to peel off from a press plate. A portion of the film sticks and remains on the press plate to obstruct successive production of circuit boards.
Thus, an object of the present invention is to provide a releasing film without the aforesaid problems.
The present invention also provides a carrier film for a coating film. The carrier film is used as a supporting film to make the coating film. To form a coating film with a uniform thickness, the carrier film must have a uniform thickness, too. After a coating film is formed by casting a resin on the carrier film, the carrier film is peeled from the coating film. Therefore, the carrier film is required to have a good releasing property. As the carrier film, a fluororesin film or biaxially drawn polyethylene terephthalate (PET) film with a silicone compound coated thereon is hitherto mainly used.
However, as mentioned above, a fluororesin is generally expensive. Therefore, a film thereof is preferably thin from an economical viewpoint, but at the same time it should not be too thin to have poor handling property. A fluororesin film thick enough to have a satisfactory handling property tends to have poor precision of thickness. This causes a problem that thickness of a coating film formed on the fluororesin film is not uniform.
Further, the fluororesin has poor mechanical strength such as tensile strength and may be torn when stretched in a coating process line. Meanwhile, a PET film coated with a silicon compound has a disadvantage that a coating film formed thereon is contaminated with the silicone compound.
Thus, an object of the present invention is to provide a carrier film for a coating film without the aforesaid problems.
The present invention is a releasing laminated film comprising a supporting film having a tensile modulus of elasticity in a traverse direction measured according to ASTM D882 of 980 to 6,860 N/mm2 and at least one film comprising a fluororesin laminated on at least one side of the supporting film.
Further, the present invention is a releasing laminated film comprising a supporting film having a tensile modulus of elasticity in a traverse direction measured according to ASTM D882 of 980 to 6,860 N/mm2 and a film comprising a fluororesin laminated on one side of the supporting film, the other side of the supporting film having a 10-point averaged surface roughness (Rz) of 3.0 to 8.0 xcexcm and the number of peaks (Pc) of 200 to 400 measured according to JIS B0 601.
Preferably, said Rz is 4.0 to 7.0 xcexcm and said Pc is 250 to 350.
Preferably, said tensile modulus of elasticity in a traverse direction is in a range of from 2,940 to 5,880 N/mm2.
In the preferred embodiments, the fluororesin is tetrafluoroethylene-ethylene copolymer resin and the film comprising the fluororesin has a thickness of 1 to 50 xcexcm; the supporting film has a melting point of 110xc2x0 C. or higher; and the supporting film is a polyester film having a thickness of 5 to 1,000 xcexcm.
The present invention also provides a laminated carrier film comprising a drawn polyester film and a film comprising a fluororesin laminated on at least one side of the drawn polyester film, the carrier film having a difference between a maximum thickness and a minimum thickness (R) of 5 xcexcm or smaller, wherein R is measured along a 10 cm-long line starting at an arbitrary point on a surface of the laminated film with a continuous-mode thickness meter provided with a tip having a diameter of 5 mm.
In the preferred embodiments, said R is 3 xcexcm or smaller; the drawn polyester film is a polyethylene terephthalate film having a thickness of 5 to 1000 xcexcm; and the film comprising a fluororesin is a tetrafluoroethylene-ethylene copolymer film having a thickness of 2 to 10 xcexcm.
In the films described above, it is preferred that the film comprising a fluororesin is dry laminated on the supporting film.
Preferably, in the films described above, a polyethylene film, polypropylene film, or polyester film is further laminated on the film comprising a fluororesin.
Preferably, the film described above has a total thickness of 10 to 300 xcexcm, more preferably 60 to 300 xcexcm.